The present application is based on and claims priority from the following Japanese Patent Applications: 2000-203502, filed Jul. 5, 2000; 2000-203550, filed Jul. 5, 2000; 2000-255288, filed Aug. 25, 2000; 2000-255498, filed Aug. 25, 2000; and 2000-256267, filed Aug. 25, 2000; the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a vehicle passenger sensing system that includes a plurality of pressure sensing cells disposed in a vehicle passenger seat to sense presence of a passenger.
2. Description of the Related Art
In a vehicle that is equipped with a passenger""s air bag, it is necessary to sense presence of a passenger seated on a passenger seat in order to prevent a passenger""s air bag from inflating when no passenger is seated on the seat.
Even if a passenger system senses the presence of a passenger and the passenger""s air bag operates properly at a certain accident, such an air bag may harm the passenger if the passenger is a child or a baby.
Therefore, it is necessary to sense whether the passenger is a child or not. Although, weight sensing is generally useful, mere weight sensing cannot tell whether the passenger is a child or not if a seat is reclined to a laid down position. If a child seated on a child seat is fastened to the passenger seat, the sensed weight is heavier than the child""s weight.
Therefore, a main object of the invention is to provide an improved passenger sensing system that can correctly tell whether a passenger is a child or not.
Another object of the invention is to provide a passenger sensing system that can correctly sense the weight of the passenger from a plurality of weight sensing cells regardless of deviation in the sensitivities of the sensing cells.
A method of calibrating sensitivities of a plurality of pressure sensing cells disposed at a passenger seat to detect presence of a vehicle passenger according to a main aspect of the invention is comprised of the following steps: pressing a presser against the passenger seat; detecting output signal levels of the sensing cells; and adjusting sensitivity of the pressure sensing cells according to the output signal levels while the presser is pressed against the seat.
The step of pressing may be comprised of a step of applying equal pressures on all the sensing cells and a step of removing the pressures. The presser may be a flexible bag filled with liquid. The flexible bag may have a surface area sufficient to apply the pressure on all the sensing cells concurrently. The flexible bag may be comprised of a plurality of portions for separately applying pressures on a middle of the seat and sides of the seat.
The method according to the main aspect of the invention may be comprised of a step of estimating final output signal levels before the step of adjusting. The step of estimating may be comprised of a step of estimating a change in output signal level of the sensing cells when the passenger seat is pressed by the presser. The step of estimating may be comprised of a step of estimating a final output signal level according to a response relationship between pressure applied to the sensors and output signal levels of the sensor. The final output level may be estimated according to a decreasing rate of output signal level of the sensing cell.
In the method according to the main aspect of the invention, the step of adjusting may be comprised of separate steps of adjusting respective sensing cells.
In the method according to the main aspect of the invention, the steps of pressing, detecting and adjusting may be carried out for those of the sensing cells disposed at predetermined sections of the passenger seat.
In the method according to the main aspect of the invention, the step of adjusting may be comprised of a step of dividing the passenger seat to a plurality of sections, and a step of applying different weight of importance to each different section to provide a value to correct sensitivity of the each section.
In the method according to the main aspect of the invention, the step of adjusting may be comprised of a step of dividing the passenger seat to a plurality of sections, and a step of correcting sensitivity of the sensing cells of each section.
In the method according to the main aspect of the invention, the presser may be comprised of a bag having a contact surface fitted to the surface of the passenger seat. The presser may be formed of a plurality of bags having a contact surface fitted to the surface of each section of the passenger seat.
In the method according to the main aspect of the invention, the step of detecting may be comprised of a step of detecting a shift of a distribution pattern of output signal levels of the sensing cells, and the step of adjusting may be comprised of a step of correcting the shift according to the output signal levels.
In the method according to the main aspect of the invention, the presser may be comprised of means for profiling a surface of passenger""s buttocks. The means may be comprised of a plurality of pistons having edges, each of which is controlled to follow a portion of the surface of passenger""s buttocks.